Rapid development of modern industries, and constant increase in the number of automobiles have caused an evergrowing concentration of carbon dioxide (CO2) in atmosphere, and further lead to environment pollution and extreme climates, which have been drawing increasing high attention of the countries in the word. Therefore, how to reduce the concentration of CO2 in atmosphere and maintain an ecofriendly one has become the global concern.
George Andrew Olah, the famous organic chemist and Nobel Prize winner of chemistry, had proposed the concept of “Methanol Economy”, that is, CO2 captured from the atmosphere catalytically reacts with hydrogen prepared by using non-fossil energy to synthesize methanol, which can serve as the energy to reserve instead of fossil energies, as fuels itself and as raw material in the synthesis of hydrocarbons and their down-stream products. Methanol Economy will be an effective solution to oil gas and energy problems in the future. (J. Org. Chem., 2009, 74(2): 487-498.) Nobel Prize winner of physics, Carol Rubbia, had also proposed to use a procedure of preparing methanol through CO2 hydrogenation to replace the currently popular capture and storage of carbon, so as to reduce emissions and meanwhile provide raw materials to the development of the industry. US Carbon Science Inc. has put forward a three-step procedure to produce a fuel oil with CO2, wherein CO2 in flue gases is used as a raw material, and saline electrolysis is used to provide necessary hydrogen.
There are numerous correlated studies and reports on the technology of synthesis of methanol through hydrogenation of CO2 over the world. However, this technology has still been confronted with some technical difficulties for industrialization thereof, among which the most important comes to research in the development of high-performance catalysts. It is not easy for CO2 to participate in a chemical reaction because the chemical-bond energy of CO2 is rather high. As a result, it is necessary for the reaction in synthesis of methanol through CO2 hydrogenation to be performed in the presence of a high-performance catalyst. Conventional catalyst Cu—ZnO—Al2O3 used in synthesis of methanol does not present very high performance while being used in CO2 hydrogenation to methanol. It is widely believed that, the active precursor of a Cu—ZnO-based catalyst used in CO (or CO2) hydrogenation to methanol should be in the form of a Cu—Zn double salt before being roasted, including (Cu,Zn)2CO3(OH)2 (rosasite crystalline phase) and (Cu,Zn)5(CO3)2(OH)6 (aurichalcite crystalline phase). The crystalline phase in the precursor of the catalyst prepared through the conventional coprecipitation method and used in synthesis of methanol, before being roasted, is substantially in the form of the rosasite crystalline phase (J. Mol. Catal., A-Chemical, 2013, 366: 48-53.), which, as the active precursor used in synthesis of methanol through CO2 hydrogenation, is not an optimum active precursor in the synthesis of methanol through CO2 hydrogenation although presents catalytic performance to a certain degree. There are also some researchers believe that, due to generation of a large amount of water in the synthesis of methanol through CO2 hydrogenation, and hydrophilic nature of Al2O3, the catalyst, readily influenced by the molecules of water, would have decreased mechanical strength, modified active sites, etc. (J. Catal., 2007, 249(2): 185-194.) Therefore, the studies on improvement of catalytic performance of copper-zinc-based catalysts in the synthesis of methanol through CO2 hydrogenation mainly focus on the preparation method of the catalysts, and on selection of promoters and carriers. The purpose thereof is to enable controlling over formation of the crystalline phase of the active precursor of the catalyst used in the synthesis of methanol through CO2 hydrogenation, and to improve catalytic performance and hydrothermal stability of the catalyst.